In a method for performing highly precise time synchronization between communication equipments, for example, a precision time protocol (PTP) is used. When such a time synchronization method is employed, a plurality of line interface cards mounted in a single transmission device operates in synchronization with a common reference timing. Therefore, a pulse signal generated in a common timing generation card is cyclically transmitted to each of the line interface cards via a back wired board (BWB), which is a wiring substrate.
Regarding signal transmission between devices, for example, Japanese Laid-open Patent Publication No. 11-225173 describes a point that a signal is returned to a transmission path at a reception side to calculate a transmission delay of the signal and delay adjustment is performed.
As a method for synchronizing reception timings of pulse signals among the plurality of line interface cards, for example, a method in which the wiring length of the BWB is made the same between the timing generation card and each of the line interface cards may be used. However, in the BWB, in order to wire signal lines such that each of signal lines for pulse signals avoids other signal lines and the signal lines of pulse signals have the same wiring length, for example, the number of layers of a substrate of the BWB is increased. This causes increase in device cost.
Instead of using the method above, a method in which a transmission delay between the timing generation card and each of the line interface cards is measured and a delay of a corresponding pulse signal is individually adjusted in accordance with a measured value obtained in the measurement may be used. Using this method, synchronization of reception timings of pulse signals is realized without increasing the device cost.
However, assuming a case where techniques described in Japanese Laid-open Patent Publication No. 11-225173 is employed, when a signal is returned at a tip of a transmission line, a delay time of a signal, which is generated by a delay adjustment buffer, is unknown. Therefore, precise delay adjustment is not possible.